It is known, e.g. from U.S. Pat. No. 3,158,380, to interpose a metallic annular spacer between two flange surfaces and to insert an elastic sealing ring in an annular groove on each face of that spacer, the body of the spacer being split along its inner periphery by a radially extending annular channel into a pair of resilient lips respectively carrying these sealing rings. The pressure of the fluid entering the channel urges the sealing rings into contact with the adjoining flange surfaces. The sealing rings, consisting of rubber or the like, initially have a corrugated profile which is flattened against the spacer faces under pressure of clamping bolts that hold the two flanges together and traverse the spacer in a marginal zone lying radially outwardly of the sealing rings.
A joint of this description, employing elastomeric sealing rings, can be used only at relatively low temperatures. With conduits carrying hot fluids it would be necessary to make the rings of relatively soft metal, e.g. silver, copper or lead, if the flanges and the spacer consist of steel as is usually the case. Even then, however, proper functioning is not assured since even high clamping pressures will not necessarily distribute the material of the deformed sealing rings with sufficient uniformity within their annular grooves to prevent leakages. It has therefore been the practice in such instances to interpose a spacer with a sawtooth profile between the flanges and to separate that spacer from the flange surfaces by annular washers of relatively soft metal into which the sawteeth bite under pressure. Such a joint generally requires very high clamping pressures while still not guaranteeing fluidtightness in all instances.